WinAVR (pronounced "whenever") is a suite of executable, open source software development tools for the Atmel AVR series of RISC microprocessors hosted on the Windows platform. It includes the GNU GCC compiler for C and C++.
WinAVR contains all the tools for developing on the AVR. This includes avr-gcc (compiler), avrdude (programmer), avr-gdb (debugger), and more! WinAVR is used all over the world from hobbyists sitting in their damp basements, to schools, to commercial projects.
Willem EEPROM Programmer is a very useful programmer software that can program EPROM, EEPROM, FLASH, Serial EPROM, Serial Flash and more(Vpp 3.6V, 12.5V, 21V, 25V) and supports CHIPS (EPROM, EEPROM, FLASH, I2C, PIC, MCS-51, AVR, 93Cxx, ISP) and more.
SDCC is a retargettable, optimizing ANSI - C compiler that targets the Intel 8051, Maxim 80DS390, Zilog Z80 and the Motorola 68HC08 based MCUs. Work is in progress on supporting the Microchip PIC16 and PIC18 series. SDCC is Free Open Source Software, distributed under GNU General Public License (GPL).